High Temperature Oxidation Behavior of Laser Clad NiCrAlY Layer

As for plants, higher operation temperature is required so as to attain higher efficiency.The plant construction material requires not only good mechanical property at higher temperature but also better oxidation resistantce. It has become difficult to satisfy these requirements simultaneously by a single bulk material.One of the countermeasures is surface treatment such as PTA (Plasma transferred arc weldinhg), CVD (Chemical vapor deposition), PVD (Physical vapor deposition) and so on. Among surface treatment laser cladding is one of the outstanding methods because its higher power density enables to clad refractory materials or even ceramics. However, there has been little work on the oxidation behavior of laser clad NiCrA1Y layer.Therefore the oxidation behavior of laser clad NiCrAlY layer formed with single layer so as to take account of the influence of dilution from the substrate. Influence of Al content and heat treatment were also investigated.The results obtained are as follows;(1) The oxide formed on the NiCr10A1Y and NiCr20AlY clad layers was mainly α-Al2O3 and the growth rate of the oxide obeys parabolic rate law.(2) The parabolic rate constant of the NiCr10AlY clad layer is approximately the same with that of the bulk material, but that of the NiCr20AlY clad layer is larger by 1-2 orders of magnitude. The difference in parablic rate constant is caused by the formation of unstable faster growing θ-Al2O3 on NiCr20AlY clad layer at the initial stage of the oxidation.(3) The heat treatment makes the distribution of aluminum in the clad layer more homogenious which enhances the nucleation of Al2O3 at the initial stage of the oxidation, resulting in the lower parabolic rate constant.